The only answer we know for sure is things are changing

the lodestone post we got today was very unclear as to what is being changed/removed EXCEPT for the fact the achievments are going

primals may still be here
dungeons too

what may be happening is the fights are changing(due to new mechanics of the game specificaly) so they are adding new achievemnts for them and removing the old?

we dont know, we could use some clarification for sure on what is actualy going to be gone or if its just the achievemnts themselves